Generally, the membrane used in a membrane based separation process is susceptible to fouling. The fouling occurs only on one side of the membrane i.e., on the feed side of the membrane in membrane based separation process such as ultra-filtration (UF), micro-filtration (MF), nano-filtration (NF) and reverse osmosis (RO). This is due to the fact that, only the feed side of the membrane gets exposed to salt water, while the other side i.e., the draw solute side of the membrane is exposed to pure water. Therefore, monitoring of membrane fouling and providing optimization solution in respect of the membrane fouling process is oriented towards one side of the membrane due to the fouling occurring on one side of the membrane.
However, in membrane based separation process like forward osmosis (FO), pressure retarded osmosis (PRO), etc., fouling occurs on both the sides of the membrane, with the membrane being exposed to salt water on both sides but with different levels of salt concentration. For instance, in pressure retarded osmosis process the pretreated river/brackish water or the feed solution is supplied at feed side of the membrane and pretreated sea water or draw solution is supplied at draw water solution side, and it is vice versa in forward osmosis process. The feed and draw solution can also come from different sources, e. g, when pressure retarded osmosis is coupled with desalination process, concentrated brine of sea water desalination process or reject sea water can be used as a draw solution and the pretreated sea water/brackish water can be used as a feed solution.
Practically, both the sea water and river water contains micro organisms, organic and inorganic contents that causes fouling/scaling at both the sides of the membrane surface. The membrane blockage due to micro organism and organic content is called as fouling and the membrane blockage due to inorganic content is called as scale. Therefore the word fouling and scaling are interchangeable in this context. The intensity of fouling will be different on one side of the membrane surface with respect to the other depending upon the type of water i.e., sea water or river water, to which the corresponding side/surface of the membrane is exposed to. Accordingly, the surface of the membrane exposed to sea water is subjected to fouling at a larger scale as compared to the other side that being exposed to river water or vice versa and it will depend on quality of water source. Therefore, it becomes imperative to monitor and control fouling of the membrane on both the sides, so as for the membrane separation process to be efficient.
The rate of fouling at both the sides of the membrane is affected by operating conditions of the membrane such as water flux across the membrane, head between feed and draw solution side of the membrane etc. Hence there is a need for a solution that provides online monitoring and control of fouling and provides optimization thereof in relation to two sides of the membrane.
The invention is aimed at providing a solution that caters to the need for online monitoring and control of fouling, and of the optimization thereof of two side membrane processes.